The purpose of this study is to gain an understanding of the mechanism of carcinogenesi. It is particularly pertinent to this broad objective that we have great experience with a naturally occurring metabolite, methionine, and its analogue, ethionine. The resemblance of ethionine to methionine in chemical structure and pathways of cellular metabolism gives a study of ethionine carcinogenesis an advantage over other carcinogens. Because ethionine is carcinogenic, it provides an unusually important tool for offering us an insight into the possible mechanism of carcinogenesis otherwise not available. In the proposal, experimnts are featured which use some inhibitors of lesion formtion in liver. It was found that 1,10-phenanthroline and some other related substances are very effective protectors in liver offatty liver formation, ductular and mesenchymal cell proliferation and fibrosis and later on, hyperplastic nodule and hepatoma formation. These findings made possible the search for the point of inerference with the metabolic pathway of ethionine. Because these substances do not intervene substantially with the early metabolic reactions of etionine (drop in ATP and formation of S-adenosylethionine) which are generally observed as a keypoint of ethionine action, an investigation of later decisive mechanisms of ethionine action at a high level of molecular-biological hierarchy is encouraged.